A phase shifter changes a phase difference (pass phase) between an input signal and an output signal by controlling a voltage and the like supplied to a control terminal. The phase shifter is used for phase adjustment in a circuit, for example. The phase shifter is applied to, for example, a predistorter for phase distortion, a phased array antenna and the like. As the phase shifter, one with a configuration using a transmission line (for example, refer to Patent Document 1), and one with a configuration using inductors (for example, refer to Patent Document 2) are known.
A differential circuit configuration is generally employed in an analog circuit such as an amplifier and a mixer. The differential circuit can reduce an influence of element variance and a power supply noise, so that it is widely used in a semiconductor device. Meanwhile, a single-phase signal is preferable when a signal is transmitted to an exterior of the semiconductor device, because of a reason such that a number of terminals is limited, and it is difficult to configure an equal-length wiring in the exterior of the semiconductor device. For this reason, it is performed to convert a single-phase signal into a differential signal, and to convert a differential signal into a single-phase signal in the semiconductor device.
There is a balun, as one of circuits conducting a single-phase-differential conversion. The balun is realized by connecting one side of a transformer to a reference potential. In the balun, since a primary side and a secondary side of the transformer are coupled only by a mutual induction of inductors, it is possible to separate the reference potential, and the balun is used for the single-phase-differential conversion. The single-phase-differential conversion realized by the balun causes a low loss and a small distortion, so that the balun is used for a single-phase-differential conversion of input and output signals in an amplifier circuit and the like in which low distortion and high gains are demanded, for example. On the other hand, a transformer and inductors configuring the balun occupy a large area and thus an integration thereof is difficult, resulting in that an occupied area in a semiconductor device increases.
[Patent Document 1] Japanese Laid-open Patent Publication No. 06-69701
[Patent Document 2] Japanese Laid-open Patent Publication No. 62-278813
For example, it is considered to control a pass phase by using, in a differential circuit, a phase shifter with the configuration using the transmission line or the configuration using the inductors described above. For example, the configuration using the transmission line as the phase shifter disclosed in Patent Document 1 uses a (λ/4) transmission line, so that a large area becomes necessary for realizing the phase shifter. For example, when a phase shifter dealing with a signal of 2 GHz used for wireless communication and the like is employed, a λ/4 becomes 3.75 cm in a vacuum. A wavelength shortening ratio realized by a dielectric is about 0.3 times at the most even on a dielectric substrate and the like, so that a length of a transmission line is 1 cm, resulting in that an area is increased and it is difficult to realize an integration. In the configuration using the inductors as the phase shifter disclosed in Patent Document 2, for example, since two inductors are added to be used, a circuit area and a number of parts are increased.
With respect to such problems, a phase shifter using resistors and variable capacitors is proposed (for example, refer to Patent Document 2). In the configuration of using the resistors and the variable capacitors as the phase shifter, an increase in a circuit area can be suppressed, but, a loss is increased due to the resistors. If, as a countermeasure against this, an amplifier for compensating the loss is used, a consumption current is increased, in addition to the increase in the circuit area and the number of parts.